Dear Pedro,
On 13 May 2012, at 20:29, José Pedro Magalhães wrote:
> On Fri, May 11, 2012 at 5:12 PM, "Philip K. F. Hölzenspies"
> <p...@st-andrews.ac.uk> wrote:
>
> However, it turns out that this never leads to an evaluation of
> extTyNamesLoc. I've come as far as to see that, since "Located a" is a
> synonym for "GenLocated SrcSpan a", the type we're looking for really has a
> binary constructor, thus we should use ext2Q.
>
> This made things work: We first modify the function we apply to Located
> things:
>
>
> extTyNamesLoc :: (Data loc, Data a) => SrcSpan -> GenLocated loc a ->
> OccurrenceTable
> extTyNamesLoc l (L l' x) = case cast l' of
> Just l'' -> extTyNames l'' x
> Nothing -> extTyNames l x
>
> Do you really need this? Can't you use the definition of `extTyNamesLoc`
> shown previously, and redefine `extTyNames` to use `ext2Q`, as in:
As it turns out, yes I do. You had me doubting whether I had tried this, but
doing such a thing gives me:
refact.hs:124:72:
Could not deduce (d1 ~ SrcSpan)
from the context (Data a)
bound by the type signature for
extTyNames :: Data a => SrcSpan -> RefCtx -> a -> OccTab
at refact.hs:124:1-91
or from (Data d1, Data d2)
bound by a type expected by the context:
(Data d1, Data d2) => GenLocated d1 d2 -> OccTab
at refact.hs:124:21-88
`d1' is a rigid type variable bound by
a type expected by the context:
(Data d1, Data d2) => GenLocated d1 d2 -> OccTab
at refact.hs:124:21
Expected type: GenLocated d1 d2 -> OccTab
Actual type: Located d2 -> OccTab
In the return type of a call of `extTyNamesLoc'
In the second argument of `ext2Q', namely `extTyNamesLoc l r'
Which makes a certain amount of sense. The use of ext2Q binds d1 and d2 to be
restricted to Data, but otherwise unspecific. This seems at odds with the
intention of extXY, hence my confusion.
I have since found and come to understand extB, though. This makes the
implementation of extTyNamesLoc much, much nicer. However, I still think
finding a good explanation for the behaviour of ext1Q/ext2Q could lead to a
helpful addendum of the SYB documentation.
Regards,
Philip_______________________________________________
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